This H-bridge variant was
one of the first in which the reversing circuitry is built
into the driver, rather than (as is more-commonly done) into
the control circuitry upstream of the driver. This is a
handy circuit, though, for 2-motor walkers -- as all that is
required to reverse one is to reverse the phasing of one of
the motors.

Wilf revisited this design in Yahoo group post
#31505; he adds (since the CD4016 is an obsolete part,
and unlikely to be found) "If you use Vcc
> 3V or use a 74HC4066 instead of the CD4016
then add a 220 - 1K resistor
in series with the base
of each 2N2907. "